1. Field of the invention
This invention relates to a magnetic storage apparatus used for computers and information processing apparatuses, and more particularly relates to a magnetic head and a magnetic storage apparatus suitable for a perpendicular magnetic recording medium obtained realizing a high density recording.
2. Description of the prior art
Information processing apparatus employs mainly semiconductor memory and magnetic memory as their storage apparatus. Semiconductor memory is used mainly for the internal storage apparatus in view of access time , and magnetic memory is used mainly for external storage apparatus in view of large capacity and non-volatility.
Recently, magnetic disk and magnetic tape have been mainly used as magnetic memory. A recording medium used for these magnetic memory comprises an Al substrate or resin tape on which a magnetic thin film is formed. To record magnetic information on the recording medium, a functional component having electromagnetic conversion function is used. To reproduce magnetic information, a functional component which utilizes magnetoresistive phenomenon, giant magnetoresistive phenomenon, or electromagnetic induction phenomenon is used. The functional component is incorporated in an input/output unit so-called a magnetic head.
A magnetic head and a recording medium are moved relative to one another, and have a function to record magnetic information on the arbitrary position of the medium and to reproduce electrically magnetic information as required.
As shown in FIG. 2, a magnetic head comprises , for example, a recording component 21 for recording magnetic information and a reproducing component 22 for reproducing magnetic information.
The recording component 21 comprises a coil 26 and magnetically coupled magnetic poles 27 and 28 located so that the coil 26 is sandwiched therebetween.
The reproducing component 22 comprises a magnetoresistive effect unit 23 and a pair of an electrode 29 for supplying a constant current to the magnetoresistive effect unit 23 and for detecting resistance change.
Between the recording component 21 and the reproducing component 22, a magnetic shield layer 28 (served also as the write pole) is provided. These functional components are formed on a magnetic head body 30 through a primary layer 24 and shield layer 25.
The example shown in FIG. 2 utilizes electromagnetic conversion function for recording and utilizes magnetoresistive effect for reproducing. However, the reproduction of magnetic information may be performed by detecting electromagnetic induction current induced in a coil provided in a recording component. In this case one component is served for both recording and reproducing.
The performance of a storage apparatus depends on the input/output operation speed and storage capacity, as a result, short access time and large storage capacity are essential to render the product competitive. Recently small sized storage apparatus have been developed in response to the request for compact information apparatus. To satisfy this request, development of a magnetic memory device for recording and reproducing much magnetic information in and from a single sheet of recording medium is important.
To satisfy this request, it is required to increase the recording density of a magnetic memory device. To increase the recording density, it is required to miniaturize the size of domain which is the source of magnetic information. It is also required to increase the frequency of recording current supplied to the coil 26 shown in FIG. 2 and to narrow the design of the width W of recording magnetic pole 27.
According to the examination performed by the inventors, a recording pole width W of 2.5 xcexcm and a recording frequency of about 90 MHz realized a recording density of 2Gb/in2 class. However, it was found that an even higher density caused a problem and revealed the limitation of high density recording.
Heretofore, magnetic films called longitudinal media of in-plane magnetization direction have been used as recording media. In an in-plane medium, the boundary between domains is mainly magnetized, and the magnetization is read out by detecting field intensity. Because the magnetization is concentrated, a signal of Gaussian shape (Lorentzian shape) pulse signal is outputted. Since the frequency band contained in a signal is narrow, it is less susceptible to the deterioration of signal quality due to neighboring signal. Therefore, signals are processed easily thereafter.
However, thermal fluctuations of magnetization is an inevitable problem in development of high density recording using an in-plane medium. The thermal fluctuations are due to thermal fluctuations of magnetization in a recording medium, and the thermal fluctuations are caused by increasing miniaturization of domains because the demagnetizing effect of neighboring domains become remarkable and the magnetization direction becomes unstable.
According to experiments conducted by the inventors, it was confirmed that domains could be erased due to thermal fluctuation when density was increased as high as to about 400 kbPI (bits per inch) in the circular direction and about 26 kTPI (tracks per inch) in the radius direction.
The perpendicular magnetic recording is known as a technology for preventing the problem. Because demagnetization of neighboring domains function so that fluctuations width of magnetization due to thermal fluctuation are decreased, the domain erasing phenomenon due to thermal fluctuation is less susceptible. Therefore, the perpendicular magnetic recording is expected to be the high density recording technology of the future.
However, because magnetic charges are distributed on the medium surface in the perpendicular magnetic recording, if magnetization is reproduced using a reproducer used for detecting field intensity of a conventional longitudinal medium as shown in FIG. 2, square wave (dipulse) is detected depending on domain width. Such a square wave requires complex signal processing because of wide band. Such complex signal processing requires use of a complex electric circuit. Therefore, it is difficult to realize an inexpensive and high speed apparatus, and as a result, this problem is one of the reasons for slow commercialization of perpendicular magnetic recording.
The above-mentioned problem will be solved if output signals obtained from perpendicular media are of Gaussian shape similar to conventional longitudinal media.
Accordingly, it is the object of the present invention to provide a magnetic head and a magnetic recording apparatus using the magnetic head having a novel reproducing means which is capable of outputting reproducing signal obtained from a perpendicular magnetic medium as a Gaussian shape pulse signal. The present invention realizes a high speed and high density magnetic recording apparatus which utilizes a perpendicular magnetic recording method.
In order to realize the above-mentioned object, the magnetic head and the magnetic recording apparatus using the magnetic head of the present invention use means described hereinafter.
The first embodiment uses a perpendicular magnetization film having an easy magnetization axis perpendicular to the direction of the film surface, and the first embodiment is provided with at least a magnetic head having a function for recording and reproducing information. Particularly in the magnetic head, a reproducing means for having reproducing function of information is provided with piled up or stacked two spin valve elements with a pinned layers having magnetization direction difference of about 180 degrees, and recorded information is reproduced from the perpendicular magnetization film.
In detail, the object of the present invention is accomplished by providing a magnetic recording apparatus provided with a perpendicular magnetic recording medium having an easy magnetization axis in the direction perpendicular to the longitudinal surface, and a magnetic head having both recording and reproducing function of information, wherein the magnetic head is structured with a reproducing means comprising piled two (the first and second) spin valve elements having at least a magnetoresistive elements for performing reproducing function, and the magnetization direction of the pinned layers which are components of each spin valve element are different by about 180 degrees from each other.
Both ends of two (first and second) spin valve elements respectively provided with a magnetoresistive element is connected commonly and an electrode is provided to each terminal, and operation of read out (reproducing) means is performed by connecting a constant voltage power source or constant current power source to an electrode.
Preferably pinned layers of the piled two spin valve elements comprises respectively an antiferromagnetic film, and a blocking temperature difference of the respective antiferromagnetic films is prescribed to be 20xc2x0 C. or larger. The blocking temperature will be described hereinafter.
Alternatively, pinned layers of the piled two spin valve elements comprise a high coercive force film, and a coercive force difference of the respective high coercive force films is prescribed to be 100 Oe or lager.
A current terminal of the first spin valve element and a current terminal of the second spin valve element are connected commonly, and an electrode is provided on the common point. Thereby two elements function as a single device.
Alternatively, the first spin valve element and the second spin valve element are maintained electrically insulated, connected so that output from the elements is in differential mode, and supplied with a current.
In the above-mentioned case, a dual spin valve element having the first spin valve element and the second spin valve element provided with a single oxide antiferromagnetic film inserted therebetween is structured.
The above-mentioned reproducing means is incorporated in a magnetic head slider, and provided partially on an air bearing surface at least near a perpendicular magnetic recording medium.
In the above-mentioned reproducing means, the respective spin valve elements are piled up closely, and a soft magnetic pattern is provided between these spin valve elements on the side distant from the air bearing surface. The soft magnetic pattern forms a magnetic circuit from the first spin valve element to the second spin valve element.
The second means to accomplish the above-mentioned object is a magnetic recording apparatus comprising a perpendicular magnetic recording medium having an easy magnetization axis in the direction perpendicular to the film surface and a magnetic head having both functions for recording and reproducing information. The reproducing function of the magnetic head is given by a reproducing means provided with the first spin valve element and the second spin valve element piled up with interposition of a spacer film which spin valve elements at least comprise a magnetoresistive element, the first spin valve element comprises the first ferromagnetic film, the first non-magnetic medium layer, the second ferromagnetic film, the second non-magnetic film, and third ferromagnetic film placed one on another in this order or in inverse order, and functions thereby so that the first ferromagnetic film and the second ferromagnetic film exert exchange interaction each other so as to direct the magnetization direction of the respective ferromagnetic films in inverse direction, and the difference in magnetization direction between the second ferromagnetic layer and the third ferromagnetic layer generates magnetoresistive effect. The second spin valve element comprises the fourth ferromagnetic film, the third non-magnetic medium layer, and fifth ferromagnetic film placed one on another in this order or in inverse order, and functions thereby so that the difference in magnetization direction between the fourth ferromagnetic film and the fifth ferromagnetic film generates magnetoresistive effect.
Both ends of two (first and second) spin valve elements respectively provided with a magnetoresistive element are connected commonly and an electrode is provided to each common point, and operation of read out (reproducing) means is performed by connecting a constant voltage power source or constant current power source to an electrode.
In the structure of the spin valve element, the first non-magnetic medium layer comprises a layer with a thickness of 1.5 nm or thinner consisting of any one of metal layers selected from a group of Ru, Rh, Ir, Cr, and Cu or consisting of an alloy containing some of these metals. The first non-magnetic medium layer is sandwiched between ferromagnetic layers to generate a strong antiferromagnetic exchange interaction between these ferromagnetic layers. As a result, the magnetization direction of the first ferromagnetic layer and the magnetization direction of the second ferromagnetic layer are always in antiparallel relation to each other.
The above-mentioned second non-magnetic medium and third non-magnetic medium layer comprise a Cu layer.
The product of the film thickness and saturation magnetization of the first ferromagnetic film is prescribed to be larger than the product of the film thickness and saturation magnetization of the second ferromagnetic film.
Further, a spacer film for separating the first spin valve element from the second spin valve element is sandwiched between the third ferromagnetic film and the fourth ferromagnetic film, and the third ferromagnetic film and the fourth ferromagnetic film are both comprise a soft magnetic film.
The magnetization of the first ferromagnetic film and the fifth ferromagnetic film are prescribed to be in the same direction.
The above-mentioned first ferromagnetic film and the fifth ferromagnetic film are structured so that the magnetization direction is specified by the antiferromagnetic film or hard magnetic film which is in contact with these ferromagnetic films respectively.
The third means to accomplish the above-mentioned object has a structure in which, for example, the first spin valve element having an Ru film provided between the first ferromagnetic film and the second ferromagnetic film, and having a Cu film provided between the second ferromagnetic film and the third ferromagnetic film, and the second spin valve element having a Cu film provided between the fourth ferromagnetic film and the fifth ferromagnetic film and having an Ru film provided between the fifth ferromagnetic film and the sixth ferromagnetic film are provided with interposition of a desired spacer film adjacently, the reproducing function component having the above-mentioned structure is used for reproducing information.
In detail, the third means is a magnetic recording apparatus provided with a perpendicular magnetic recording medium having an easy magnetization axis perpendicular to the film surface direction and a magnetic head having both functions for recording and reproducing information. The reproducing function of the magnetic head is given by a reproducing means provided with the first spin valve element and the second spin valve element piled up with interposition of a spacer film which spin valve elements at least comprise a magnetoresistive element. The first spin valve element has the first non-magnetic medium layer between the first ferromagnetic film and the second ferromagnetic film, and has the second non-magnetic medium layer between the second ferromagnetic film and the third ferromagnetic film, and the second spin valve element has the third non-magnetic medium layer between the fourth ferromagnetic film and the fifth ferromagnetic film, and has the fourth non-magnetic medium layer between the fifth ferromagnetic film and the sixth ferromagnetic film.
An electrode is provided respectively on both ends of the two spin valve elements , and operation of read out (reproducing) means is performed by connecting a constant voltage power source or constant current power source to an electrode.
A preferable structure is described herein. The first non-magnetic medium layer and the fourth non-magnetic medium layer respectively comprise a layer consisting of any one of metal layers selected from a group of Ru, Rh, Ir, Cr, and Cu or consisting of an alloy containing some of these metals.
The above-mentioned second non-magnetic medium layer and third non-magnetic medium layer comprise respectively a Cu layer.
The film thickness of the first ferromagnetic film is prescribed to be thicker than the film thickness of the ferromagnetic film, and the film thickness of the fifth ferromagnetic film is prescribed to be thicker than the film thickness of the sixth ferromagnetic film.
A spacer film for separating the first spin valve element from the second spin valve element is provided between the third ferromagnetic film and the fourth ferromagnetic film, and the third ferromagnetic film and the fourth ferromagnetic film respectively comprise a soft magnetic film.
The magnetization direction of the first ferromagnetic film and the fifth ferromagnetic film are respectively structured so as to be directed in the same direction.
Further, the magnetization direction of the first ferromagnetic film and sixth ferromagnetic film is specified respectively by an antiferromagnetic film or hard magnetic film which are respectively in contact with these ferromagnetic films.